Tuesday, May 27, 2008

An accidental discovery at Vanderbilt University may well be the key to making light-emitting diodes the dominant lighting technology of the century. Up until very recently, the only way to make "white" light was to add yellow phosphors to bright blue LEDs. It wasn't quite right, though, as even the best "white" LED retained a blue tint. This week, we got the news that a chemistry grad student at Vanderbilt has stumbled on a way to make broad-spectrum white LEDs using quantum dots -- and in doing so, he may well have kicked off a revolution.

Michael Bowers was making quantum dots, tiny nanocrystals just a few dozen atoms across. Crystals at that scale often have unusual properties, and the ones that Bowers created were no exception. When he illuminated his batch with a laser, rather than the blue glow he expected, out came a rich white light, similar in spectrum to sunlight.

Bowers then took a polyurethane sealing liquid, mixed in some of his dots, and coated a blue LED. Although the resulting bulb -- pictured above -- is crude, it puts out white light. Its visible spectrum is similar to a typical incandescent bulb, but it puts out twice the light-per-watt, and lasts fifty times longer. One key reason for its efficiency is that it doesn't put out the infrared light typical of a regular light bulb; despite being much brighter, it's still far cooler to the touch. (The LED assembly still gets hot, however.) Completely by accident, Bowers had come up with a technology that possessed the quality of incandescent light, but none of its drawbacks.